An essential means for gas control in the coal mines in, for example, China is gas extraction, mainly gas extraction by drilling boreholes. As the mining work has evolved to deep mining in China, the low air permeability in the coal seams has become a dominant factor that constrains efficient gas extraction. Therefore, enhanced permeability improvement has become a key technique for improving the gas extraction effect and realizing co-mining of deep coal and gas extraction. The enhanced permeability improvement methods adopted at present mainly include two methods: one method is coal mass treatment by means of fluid machinery and fluid medium in combination, such as hydraulic slotting and hydraulic fracturing, etc.; the other method is fracturing the coal mass by means of explosive explosion, etc. Both methods can improve the air permeability in the coal seam and improve the gas extraction effect, but have their drawbacks. When a hydraulic slotting or hydraulic fracturing method is used, a water blocking effect, etc., may occur and thereby inhibit gas desorption. When an explosion method is used, planting the explosive wastes time and energy, and the explosive is a source of danger itself and brings certain threat to safe downhole production. Therefore, it is necessary to seek for an enhanced permeability improvement measure that is safe, reliable, time and labor saving, easy to implement, and low in cost. Such a measure is of great significance for improving the gas extraction efficiency and preventing coal and gas outburst in coal mines.
Researchers have demonstrated that the gas adsorption potential of a coal mass decreases as the temperature increases. The decreased gas adsorption potential is beneficial for gas desorption from the coal mass. Hence, if a temperature field can be applied to the coal mass artificially, the gas desorption from the coal mass will be promoted effectively.